The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In order to produce elements of resistant and lightweight structure, in particular for the aeronautical field, it is known to prepare a dry fabric preform comprising for example carbon fibers, which is impregnated with a resin, in particular by an injection method called “RTM” (Resin Transfer Molding).
Thus, after curing to polymerize the resin, there is obtained an element comprising fibers whose density and orientation are locally adjusted in order to obtain mechanical strength features adapted to the forces applied to this part.
In particular, it is possible to carry out, by means of this technique, a self-stiffened panel in the shape of a skin bent about an axis such as an axisymmetric shroud or an axisymmetric shroud sector, including at least one stiffener, at least partially circumferential, providing rigidity to this skin: such a skin may be used in particular in the manufacture of an aircraft motor nacelle.
In some cases, the stiffening function is ensured by an element having a constant transverse section with a substantially “T,” “Π” (Pi), or “I” shape, comprising a web (the vertical portion of the T, Pi or I) and a flange (the extended base of the section of the T, Pi or I).
In order to produce the assembly formed by the bent skin to be stiffened and the stiffener, it is known to separately produce the skin and the stiffener which are pre-cured, then assembled by a mechanical link or a gluing.
Different methods for manufacturing curved stiffeners are known from the prior art.
A draping method of flat fabric remnants is known from the prior art, which consists in draping in the shape of the curved stiffener, flat fabric pleats. However, this operation requires a large workforce, which leads to significant draping time and manufacturing costs. Furthermore, many fabric remnants are required, and the orientation of the fibers is not optimized.
It is also known to drape fabric remnants in shape. This method consists in placing on the flange of the panel of the fabric remnants manufactured in the shape defining the web. The advantage of this method is the good control of the orientation of the fibers, but the obtained panel is mechanically weak because of the assembly of the different preforms which generate discontinuities in the fibrous reinforcement.
A method for cracking and stretching the fiber is also known from the international application WO 2005/082605. This method consists in producing a preform having the section of the final geometry then in cracking the fiber and in stretching some portions of this preform in order to give it a curved shape. However, neither the cracking method of the fiber, nor the stretching method of the preform in order to give it its curved shape can be uniform over the assembly of the woven preform. Also, the fact of breaking the continuity of the carbon fiber considerably weakens the mechanical properties of the manufactured part.
The international application WO 2013/088040 discloses, for its part, a 3D weaving method by which a three-dimensional preform having localized unbinding zones is obtained, allowing the unfolding of the preform in order to give it its “T,” “Π” (Pi), or “I” shaped section. Nevertheless, these preforms have the drawback of being straight and not being able to conform to a curvature.